Titanium nitride (TiN) films are widely used in semiconductor manufacture. Titanium nitride has become an integral part of advanced metallization schemes for many ultra large scale integrated circuit (ULSI) applications. It is used for example, as a diffusion barrier against junction spiking for aluminum contacts to silicon. In addition, TiN serves as a glue layer between tungsten and inter-metal dielectrics and to preserve the junction integrity from worm hole effects during the chemical vapor deposition (CVD) of tungsten.
Almost all of the applications utilizing TiN use physical deposition methods such as reactive ion sputtering or nitridation of sputter deposited titanium in nitrogen-containing gases at high temperatures. All of these processes suffer from poor step coverage of the deposited films. In general, TiN does not have sufficient step coverage which in some applications can lead to unreliable, high leakage and high resistivity contacts. This problem is magnified for ULSI applications where sub-micron high aspect ratio contact/via holes are required.
In order to overcome this step coverage problem, CVD deposition of TiN has also been proposed. CVD of TiN is expected to give conformal step coverage because reactants or reactive intermediates diffuse rapidly along the substrate surface before reacting. TiN films deposited using titanium tetrachloride as a source gas and ammonia, hydrogen or nitrogen gas mixtures as reactive gases have been studied and evaluated for ULSI metallization in the past.
U.S. Pat. No. 4,977,106 to Smith discloses such a CVD process for the deposition of TiN using titanium tetrachloride as a source gas and either silane or SiH.sub.4 and ammonia as a reactive gas. In general, however, the reaction temperatures with these processes have been high. It is known that high temperature processes may have an adverse effect on the completed semiconductor devices. In addition, the deposited films contained small amounts of chlorine impurity which can potentially cause corrosion related failure.
In addition to these problems deposition of TiN using a process such as that disclosed in the Smith patent produces a single phase TiN film. Such a film has a high contact resistance when deposited on a silicon substrate. A separate conductive layer such as Ti must therefore be initially deposited on the silicon substrate in the formation of semiconductor contacts.
To solve the problems associated with high temperatures and impurities, metal organic chemical vapor deposition (MOCVD) of TiN films using tetrakis-dimethylamino titanium [Ti(N(CH.sub.3).sub.2).sub.4 ] (TMAT) have been proposed recently (K. Sugijama et al, SOC, Sic. 122,1545 (1975); R. M. Fix et al, MRS Smp. Proc. 168, 357 (1990). Such dialkylamino-derivatives of titanium have been known since the experiments of Bradley (Bradley et al, J. Chem. Soc., 1960, 3857) and when used as metal organic precursors permit the deposition of high purity TiN films at relatively low temperatures (i.e. 200.degree. C). In general with such CVD processes for the deposition of TiN films, TMAT is used as a titanium source gas and ammonia is utilized as a reactive gas. A problem with such processes is that step coverage of the deposited film is poor. In addition, as with the process previously described the contact resistance at the TiN/Si interface is very high and a previously deposited layer of TiSi.sub.2 is required at the contact.
There is then a need in the art for a process for conformally depositing high purity mixed phase TiN and TiSi.sub.x films having a low contact resistance at relatively low temperatures. Accordingly it is an object of the present invention to provide a process for depositing high quality and conformal mixed phase TiN/TiSi.sub.x films at low temperatures. It is a further object of the present invention to provide such a process that is suitable for large scale semiconductor manufacture. It is a further object of the present invention to provide a process for depositing mixed phase TiN/TiSi.sub.x films with metal organic chemical vapor deposition (MOCVD) or (LPCVD) using tetrakis-dimethyl-amino titanium (TMAT) as a metal source and organic silane as a source of Si and N. It is yet another object of the present invention to provide a process for depositing mixed phase TiN/TiSi.sub.x films with the deposited films characterized by a low contact resistance, good step coverage and good barrier properties.